You probably know some people who are really full of themselves. You know, when they’re not just proud of their accomplishments, they also need to remind you of them regularly.

That might indicate a high degree of narcissism: grandiose ideas about oneself or an exaggerated sense of self-importance. But it also could just be a lot of confidence. An ego can indicate a healthy level of self-esteem, or it can be part of a diagnosable disorder, like Narcissistic Personality Disorder, also called NPD.

It turns out it's hard to make that judgment— for most of us, and even for psychologists. Psychologists define personality traits as characteristic thoughts, emotions, and behaviors that seem to be stable across time. Narcissism is one of many that psychologists can test for, and we all fall somewhere on the spectrum.

Some people are just a little more vain, and have a little more of an inflated, grand view of themselves than others do. This makes them less likely to respond well to negative feedback, and more likely to show less empathy and have a harder time maintaining relationships. But being a bit narcissistic isn’t all bad.

Some studies have shown that more narcissism is associated with more happiness and less anxiety, and even more creativity. And determining if someone scores high on the narcissism spectrum is actually quite easy: just ask them. A 2014 study involving over 2000 people found that a quote "single item narcissism scale"—aka just asking how well the definition applied to them, on a scale of 1 to 11— turned out to be about as accurate as much longer surveys that tried to, like dance around the issue a little more.

Surprise! Narcissists aren’t really that ashamed. After all, they think they’re great—why shouldn't they be a little narcissistic about it?

But scoring high on this trait isn't the same as having a disorder. Your personality traits are things that are generally true about you whether you’re at home, at school, or at work. But they don't determine everything about how you act.

Even the most extroverted people tend to act quiet and somber at a funeral, for example. It’s only when traits get really rigid and people become inflexible in their behaviors that psychologists start to draw the line between a trait and a disorder. Though how people develop personality disorders is still somewhat of a mystery.

There's some evidence that how narcissistic you are, like other personality traits, comes from your genes. But just like having a familial history of alcoholism doesn’t make you an alcoholic, not everyone with super narcissistic parents develops NPD. So psychologists think that environmental factors, particularly during adolescence, influence whether a trait becomes a disorder.

And still, what pushes people over that line is unclear. Like, you might have heard that spoiling kids will turn them into narcissists. And some case studies do suggest that narcissists had overly-indulgent and praising parents, or ones that were too permissive.

The problem is, some studies show the opposite— that parents of diagnosed patients were cold, authoritarian, or even lacked empathy. Trying to look at case studies to find risk factors is also difficult because you can’t determine cause and effect. Even if most NPD patients were raised the same way, that wouldn’t prove that the way their parents raised them gave them the disorder.

The only thing everyone seems to agree on is that risk factors for NPD need to be studied more. But even that’s not so straightforward, because NPD is especially tricky to diagnose. That’s because psychologists don’t diagnose personality disorders based on trait scores.

Technically, you could score 40 out of 40 on the narcissism scale and still not be diagnosed with NPD because diagnoses for personality disorders hinge on the trait being a problem. You have to be distressed by your behavior, it has to be causing some kind of impairment. And that makes diagnosing NPD tougher than other personality disorders because it’s basically someone who thinks they’re too great, which isn’t usually a distressing feeling.

So when NPD diagnoses do occur, they’re usually in conjunction with another issue the person sought help for, like substance use, or bipolar disorder. To be diagnosed, you need to show at least 5 of a list of 9 more severe symptoms of narcissism in addition to the inflated self-importance— things like demanding special treatment, manipulativeness, and the belief that you can only be understood or appreciated by particularly special people. These can take a toll on relationships and otherwise reduce a person’s well-being, even if they don’t realize the disorder is at the root of their troubles.

And diagnosis is especially tricky if someone has what psychologists call high functioning narcissism. Say, they’re holding down a job and meeting most responsibilities… they’re just really, really narcissistic. In one published case, for example, a man housed and supported several mistresses while still believing it had no effect on his relationship with his wife.

He only went to a psychologist because he was wondering whether to stay in his marriage, but the therapist felt that the effects of his narcissism on his personal life were enough to warrant a diagnosis. Such patients don’t always come to the attention of psychologists, and occasionally, the lack of broad impairment means doctors may disagree that a diagnosis is appropriate. But even when clearly diagnosable, NPD is notoriously hard to treat, since patients with inflated opinions of themselves are less likely to think they have a problem that needs resolution.

They’re also more likely to drop out of treatment for whatever else they initially came in for. And because NPD is so rarely diagnosed alone, almost no studies have tested treatments of patients with just NPD, so it’s hard to say what works. But research to date suggests that plain ol' therapy might be the best strategy.

One study that looked at 142 NPD patients getting treatment for depressive disorder found that they were more likely to respond to a treatment of just talk therapy, instead of therapy plus meds, perhaps because they felt more autonomy. So your friend who always interrupts your story to tell you a better one might be a little narcissistic. But that doesn’t mean they have NPD.

If you’re genuinely worried about them, you could try to convince them to talk to someone. But it’s best to leave diagnosis to the professionals. Thanks for watching this episode of SciShow Psych!

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